<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>棋盘</title>
    <style>
        *{
            padding:0;
            margin: 0;
        }
        body{
            display: flex;
            min-height: 100vh;
            justify-content:center;
            align-items:center;
        }
        .triangle{
            width:500px;
            height: 500px;
            background-color:peru;
            display: flex;
            flex-direction:column;
            justify-content:center;
            border-radius:100% 100% 100% 0;
            transform:rotate(-45deg)

        }
        .box{
            transform:rotate(45deg);
        }
        .box > div{
            width:auto;
            display: flex;
            justify-content:center;
            align-items:center;
            /* transform:rotate(-45deg) */
        }
        span{
            width:50px;
            height: 50px;
            border-radius:50%;
            background-color:green;
        }
        div>span:first-child,  div>span:last-child{
            background:darkred;
        }
        div:last-child > span{
            background:darkred;
        }
    </style>
</head>
<body>
   <figure class="triangle">
       <div class="box">
        <div>
            <span></span>
        </div>
        <div>
            <span></span>
            <span></span>
         </div>
        <div>
            <span></span>
            <span></span>
            <span></span>
        </div>
        <div>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
        </div>
        <div>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
        </div>
        <div>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
            <span></span>
        </div>
       </div>
      
   </figure> 
</body>
</html>